Method for filling a vertical tube with catalyst particles

ABSTRACT

A method of charging a vertical tube having an internal diameter of 50 mm or less with catalyst particles, which comprises introducing a filling aid into the vertical tube, where the filling aid comprises a flexible elongated body and the ratio of the cross section of the flexible elongated body to the cross section of the tube is from 0.003 to 0.08, and introducing the catalyst particles into the tube.

The present invention relates to a method of charging a vertical tube with catalyst particles. Such catalyst-filled tubes are employed for carrying out various catalytic gas-phase reactions. Depending on the type of catalyzed reaction, the tubes are heated from the outside or are surrounded by a heat transfer medium such as a salt melt to remove heat. The catalyst particles either consist of a catalytically active composition which has been shaped, with or without use of suitable binders, by extrusion, tableting or the like to give shaped bodies (all-active catalysts) or they comprise a catalytically active composition which is applied in the form of a shell to an inert support (coated catalysts). They can be in the form of spheres, rings, cylinders, cubes, cuboids, or other geometric bodies.

When the catalyst particles are introduced into the tube, catalyst particles can break or the catalytic active composition can be partly detached from the support as a result of mechanical stress, depending on the lateral compressive strength and the fracture strength of the catalysts used. The fragments or abraded material formed increase the density of the catalyst bed and during later operation of the tube reactors lead in a disadvantageous fashion to increased pressure drops.

It has therefore been proposed that the speed at which the catalyst particles fall during introduction into the tube be reduced by use of particular filling aids. Thus, EP-A 548 999 describes a method of charging tubes in which the catalyst particles are introduced along a string having flexible bristles which extend in the transverse direction and are located at a distance from one another.

A further method of introducing catalyst particles into a tube is described in U.S. Pat. No. 3,608,751. The filling aid used here is a flexible body, e.g. a hemp rope, to which oblique blades are affixed.

Although the known methods are well-suited to filling steam reformer tubes which typically have an internal diameter of about 10 cm, they are unsuitable for tubes having smaller internal diameters, as are customarily used for exothermic gas-phase reactions, in particular gas-phase oxidations. Just the introduction of the string bearing bristles or blades into a narrow tube is much more difficult. In addition, the bristles or blades of the known filling aids quickly lead to blocking of the tube or enmeshing of the catalyst particles in the case of small tube diameters.

It is an object of the present invention to provide a method by means of which vertical tubes having a small tube diameter, as are used for gas-phase oxidation reactions, can be charged with catalyst particles while avoiding, firstly, catalyst fracture or abrasion and, secondly, blockages and enmeshing of the catalyst particles.

We have found that this object is achieved by a method of charging a vertical tube having an internal diameter of 50 mm or less, preferably 40 mm or less, in particular from 20 to 30 mm, with catalyst particles, which comprises

-   -   introducing a filling aid (3) into the vertical tube (1), where         the filling aid comprises a flexible elongated body and the         ratio of the cross section of the flexible elongated body to the         cross section of the tube (1) is from 0.003 to 0.08, preferably         from 0.005 to 0.07 and particularly preferably from 0.01 to         0.06, and     -   introducing the catalyst particles (2) into the tube (1).

The filling aid has no elements such as bristles or blades which extend radially outward from the flexible body and whose projection onto a plane perpendicular to the longitudinal direction of the filling aid has a larger area than the cross section of the flexible body, preferably greater than half the cross section of the flexible body. When, in preferred embodiments, the filling aid has spacers extending perpendicular to the longitudinal direction of the filling aid, the area of their projection is negligible compared to the cross section of the flexible body.

It has surprisingly been found that in the case of small tube cross sections, a sufficient reduction in the velocity of descent of the catalyst particles can be achieved by an appropriate cross section of the flexible body and that additional damping elements which extend radially outward from the flexible body and could lead to enmeshing of the catalyst particles are not necessary. The braking of the catalyst particles is presumably due to excitation of transverse oscillations of the flexible body or formation of air vortices.

The flexible elongated body of the filling aid can be, for example, a string, a tape or a rope. In general, the flexible body comprises a textile string or a textile tape, e.g. braided natural or synthetic fibers such as nylon. However, ropes made of metal wires, e.g. a stainless steel rope, are likewise suitable.

In preferred embodiments, the flexible elongated body has an essentially circular cross section. The ratio of the diameter of the flexible elongated body to the diameter of the tube is preferably from 0.1 to 0.3, more preferably from 0.1 to 0.25. Suitable bodies are, for example, nylon strings having diameters of from about 2.5 to 5 mm, including noncircular cross sections, e.g. Bonder 0.5-2/5-10 mm.

As an alternative, it is possible to use filling aids whose flexible elongated body has a noncircular, e.g. rectangular, cross section. Thus, tapes having a thickness of from 0.5 to 2 mm and a width of from 5 to 10 mm can be used successfully.

The filling aid preferably has a rigid terminating element whose density is greater than that of the flexible body at its lower end. Introduction of the filling aid into the tube is aided by such a terminating element.

In a preferred embodiment, the filling aid can be uniform over the length introduced into the tube. The filling aid is then a smooth filling aid without dampers, spacers or the like. However, it has sometimes been found to be advantageous for the filling aid to have spacers which are located at a distance from one another and extend perpendicular to the longitudinal direction of the filling aid. Such spacers ensure that the filling aid always hangs essential centrally in the tube. The spacers are preferably very thin in order to minimize the risk of blockage caused by descending catalyst particles.

In general, the filling aid is withdrawn stepwise or continuously from the tube as the introduction of catalyst particles progresses, so that the lower end of the filling aid is always above the fill height of the catalyst particles in the tube.

A suitable procedure comprises:

-   -   introducing the filling aid into the tube in such a way that the         lower end of the filling aid is located at a first height,     -   introducing catalyst particles into the tube to below the first         height,     -   if desired, partly withdrawing the filling aid from the tube so         that the lower end of the filling aid is located at a second or         further height and introducing catalyst particles into the tube         to below the second or further height,     -   withdrawing the filling aid completely from the tube and filling         the tube with catalyst particles up to the final fill height.

In the simplest embodiment, the filling aid is introduced into the tube so that its lower end divides the tube length in any desired ratio, a first layer of catalyst particles is introduced into the tube to below the end of the filling aid, the filling aid is withdrawn from the tube and a second layer of (identical or different) catalyst particles is introduced into the tube. It has been found that when this embodiment of the method is employed, the pressure drop is up to 10% lower than when the tube is charged without the filling aid.

In another embodiment of the method of the present invention, the filling aid initially extends into the tube to ⅔ of the length of the tube, catalyst particles are then introduced to below the lower end of the filling aid, the filling aid is then withdrawn to ⅓ of the length of the tube, catalyst particles are then introduced to below the lower end of the filling aid, the filling aid is then fully withdrawn and the tube is then filled completely with catalyst particles. It has been found that this embodiment of the method is advantageous in the case of tube lengths of from three to eight meters. During operation of the tube reactor, the pressure drops were up to 20% lower than when charging methods in which the catalyst particles are introduced without a filling aid were employed.

In another embodiment of the method of the present invention, the filling aid initially extends into the tube over essentially the entire length of the tube. Catalyst particles are then introduced and the filling aid is simultaneously withdrawn from the tube at a rate corresponding to the increase in the fill height of the catalyst particles. It has been found that in the case of tube lengths of from three to six meters, this embodiment of the method results in a pressure drop which is up to 40% lower than when the tube is charged without a filling aid.

The catalyst particles are preferably introduced into the tube at an essentially constant speed, in particular by means of suitable filling machines. Such filling machines are generally made for simultaneously charging a plurality of tubes. They have a hopper having a plurality of chambers from which the catalyst particles are injected onto an inclined vibratory chute. When the vibratory chute is started up, the catalyst particles slide uniformly over the chute and drop through holes in the chute into the tubes located underneath.

The catalyst particles generally have a (maximum) diameter of from 2 to 15 mm, preferably from 3 to 8 mm. All-active catalysts consist of a catalytically active composition which is shaped, with or without use of suitable binders, by extrusion, tableting or other methods to give shaped bodies such as extrudates, pellets or the like. Coated catalysts comprise a catalytic composition, generally a mixed metal oxide, applied in the form of a shell to an inert support. They can be in the form of spheres, rings, cylinders, cubes, cuboids or other geometric bodies.

Such catalysts are known per se and are employed, for example, for the preparation of unsaturated aliphatic carboxylic acids or aldehydes, e.g. acrylic acid, methacrylic acid or acrolein, by gas-phase oxidation of aldehydes, alkanes or alkenes; the preparation of nitrites such as acrylonitrile, methacrylonitrile by ammoxidation of alkanes or alkenes or the preparation of aromatic carboxylic acids or anhydrides, e.g. benzoic acid or phthalic anhydride, by gas-phase oxidation of aromatic hydrocarbons such as toluene, o-xylene or naphthalene. Further catalysts are catalysts which catalyze hydrogenations of a variety of types or catalysts for the synthesis of methanol from synthesis gas.

It has surprisingly been found that when tubes are charged using the method of the present invention, a less densely packed, looser bed having a lower bulk density than when the tubes are charged without the assistance of a filling aid is produced. This results in an advantageous reduction in the pressure drop when a gas is passed through the charged tube during operation. As a result of the reduced pressure drop, compression energy can be saved during operation of the reactor, since the gas fed into the reactor has to be compressed to a lower pressure level. In addition, a looser catalyst bed has the advantage that the reaction zone in the tube is distributed over a greater length, which in the case of strongly exothermic reactions leads to smaller temperature increases in the tube under reaction conditions. On the other hand, when tubes having a greater diameter, e.g. the steam reformer tubes of the abovementioned prior art, are charged, higher ordered packings having a higher bulk density of the catalyst bed are obtained when using filling aids than when no filling aids are employed.

The invention will now be illustrated by means of examples and the accompanying drawings.

FIG. 1 shows a section through a tube into which a filling aid according to a first embodiment has been hung and

FIG. 2 shows a section through a tube into which a filling aid according to a second embodiment has been hung.

In the examples indicated below, a tube 1 is charged with catalyst particles 2. A plurality of parallel tubes 1 form a shell-and-tube reactor which is suitable for carrying out gas-phase oxidation reactions. Before charging of the tube 1, a flexible string 3 which serves as filling aid is introduced into the tube. The string shown in FIG. 1 is a smooth string without spacers, while the string shown in FIG. 2 is a string into which spacers 5 have been introduced at regular intervals. After the string 3 has been introduced into the tube 1, catalyst particles 2 are poured into the tube 1. As transport device 6 for the catalyst particles 2, it is possible to use either a vibratory chute or a conveyor belt. Furthermore, any number of tubes can be charged simultaneously by combining a plurality of transport devices operating in parallel. In this case, it is possible to use automatic unrolling devices which introduce the strings 3 into the tubes 1 and withdraw them again.

The invention is illustrated by the following examples. In the examples, the tubes are charged by means of charging machines which introduce the catalyst particles into the tubes by means of vibration from a stock vessel via a vibratory chute.

EXAMPLE 1 Comparative Example

A tube having an internal diameter of 25 mm and a length of 4500 mm is charged with 2160 g of a catalyst (ring shape; external diameter×height×internal diameter: 7×7×4 mm) without a filling aid. Charging took about 1 minute. The differential pressure established when 2000 standard l/h of air (20° C.) were passed through was then determined. Fill Differential Experiment No. height (cm) pressure (mbar)  1 370 84  2 368 96  3 370 100  4 370 94  5 365 91  6 368 108  7 377 105  8 374 95  9 365 65 10 366 93 11 366 96 12 364 105 13 364 97 14 372 87 15 375 86 16 372 89 17 380 81 18 376 85 19 384 89 20 378 93 21 360 112 22 378 84 23 377 90 24 381 91 25 375 95 26 377 90 27 375 89 28 384 88 29 381 87 30 384 90 Mean 373.20 91.73 Min 360.00 65.00 Max 384.00 112.00 Standard deviation 6.68 8.96

EXAMPLE 2

Example 1 was repeated, but a nylon string having a diameter of 4 mm and weighted at the end was allowed to hang into the tube to a depth of 2600 mm, 720 g of catalyst were introduced, the string was withdrawn so that it hung into the tube to a depth of 1200 mm, a further 720 g of catalyst were introduced, the string was removed and a further 720 g of catalyst were introduced. Charging took about 20 s for each of the layers introduced. Differential Experiment No. Fill height (cm) pressure (mbar)  1 385 71  2 380 80  3 382 69  4 380 75  5 374 84  6 378 76  7 391 72  8 387 84  9 376 74 10 375 72 11 387 72 12 382 71 13 370 89 14 388 74 15 387 69 16 390 64 17 391 69 18 378 86 19 376 76 20 375 52 21 388 67 22 394 70 23 394 71 24 386 68 25 374 77 26 384 76 27 380 67 28 385 68 29 394 72 30 385 76 Mean 383.14 72.93 Min 370.00 52.00 Max 394.00 89.00 Standard deviation 6.79 7.27

EXAMPLE 3

Example 1 was repeated, but a nylon string having a diameter of 4 mm and weighted at the end was allowed to hang into the tube to a depth of 2000 mm, 1080 g of catalyst were introduced, the string was removed and a further 1080 g of catalyst were introduced. Charging took about 30 s for each of the layers introduced. Differential Experiment No. Fill height (cm) pressure (mbar)  1 366 94  2 382 84  3 382 83  4 368 91  5 368 95  6 382 76  7 382 84  8 371 83  9 371 84 10 375 80 11 372 72 12 379 87 13 381 79 14 383 78 15 377 79 16 384 82 17 371 86 18 371 85 19 382 79 20 380 78 21 385 81 22 385 82 23 382 83 24 373 85 25 371 95 26 371 86 27 372 88 28 380 78 29 381 77 30 371 94 Mean 377.00 83.24 Min 366.00 72.00 Max 385.00 95.00 Standard deviation 5.82 5.62

EXAMPLE 4

Example 1 was repeated, but a nylon string having a diameter of 4 mm and weighted at the end was allowed to hang into the tube to a depth of 4300 mm. 2160 g of catalyst were introduced and the string was pulled continuously from the tube as charging progressed. Charging took about 1 minute. Differential Experiment No. Fill height (cm) pressure (mbar)  1 395 58  2 404 56  3 405 56  4 398 61  5 394 62  6 405 63  7 413 65  8 400 59  9 400 61 10 402 57 11 399 55 12 404 65 13 410 57 14 408 51 15 405 54 16 409 52 17 399 51 18 397 58 19 408 52 20 408 59 21 411 64 22 411 55 23 409 52 24 400 52 25 398 56 26 398 57 27 400 58 28 407 54 29 409 54 30 399 57 Mean 403.66 57.03 Min 394.00 51.00 Max 413.00 65.00 Standard deviation 5.35 4.19

It can be seen that the use of the filling string leads to a less dense (smaller pressure difference) and more uniform charge (smaller standard deviation of the differential pressure), with example 4 giving the best results.

EXAMPLE 5

50 ml of a catalyst (ring shape; external diameter×height×internal diameter: 5.5×3×3 mm) were allowed to drop into a tube having an internal diameter of 21 mm and a length of 6400 mm and the proportion of fractured catalyst particles was determined. With nylon string introduced Without (4 mm diameter; hanging in Experiment filling aid to a depth of 3500 mm) 1 15.7% 5.2% 2 12.7% 3.8%

EXAMPLE 6 Comparative Example

A tube having an internal diameter of 21 mm and a length of 6400 mm was charged with a catalyst (ring shape; external diameter×height×internal diameter; 5.5×3×3 mm) to a fill height of 6000 mm. Charging took about 4 minutes. Differential Amount Bulk pressure Experiment introduced (g) density (kg/l) (mbar) 1 1432 0.689 1146 2 1412 0.679 1185 3 1410 0.678 1174 4 1420 0.683 1180 5 1423 0.685 1178 6 1422 0.684 1175 7 1422 0.684 1188 8 1420 0.683 1169 9 1422 0.684 1172 Mean 0.683 1174

EXAMPLE 7

Example 6 was repeated, but a nylon string having a diameter of 4 mm and weighted at the end was allowed to hang into the tube to a depth of 3500 mm, 630 g of catalyst were introduced, the string was removed and a further 620 g of catalyst were introduced and the amount of catalyst was then brought to a fill height of 6000 mm. Charging took about 2 minutes for each of the layers introduced. Differential Amount Bulk pressure Experiment introduced (g) density (kg/l) (mbar) 1 1402 0.675 1151 2 1403 0.675 1099 3 1401 0.674 1114 4 1398 0.673 1115 5 1401 0.674 1112 6 1404 0.676 1127 7 1401 0.674 1109 8 1405 0.676 1142 9 1404 0.676 1128 Mean 0.675 1122

Comparison of example 6 and example 7 shows that the catalyst bed in example 7 is looser (lower bulk density) and leads to a smaller differential pressure. 

1. A method of charging a vertical tube (1) having an internal diameter of 50 mm or less with catalyst particles (2), which comprises introducing a filling aid (3) into the vertical tube (1), where the filling aid comprises a flexible elongated body and the ratio of the cross section of the flexible elongated body to the cross section of the tube (1) is from 0.003 to 0.08 and the filling aid has no elements which extend radially outward from the flexible body and whose projection onto a plane perpendicular to the longitudinal direction of the filling aid has a larger area than the cross section of the flexible body, introducing the catalyst particles (2) into the tube (1), and withdrawing the filling aid (3) during introduction of the catalyst particles (2) so that the lower end of the filling aid is always above the fill height of the catalyst particles (2) in the tube (1).
 2. The method according to claim 1, wherein the flexible elongated body has an essentially circular cross section.
 3. The method according to claim 2, wherein the ratio of the diameter of the flexible elongated body to the diameter of the tube (1) is from 0.005 to 0.07.
 4. The method of claim 1, wherein the flexible elongated body comprises a textile string or a textile tape.
 5. The method of claim 1, wherein the filling aid (3) further comprises a rigid terminating element (4) whose density is greater than that of the flexible body.
 6. The method of claim 1, wherein the filling aid (3) further comprises spacers (5) which are arranged at a distance from one another and extend perpendicular to the longitudinal direction of the filling aid (3).
 7. The method of claim 1, which comprises successively: introducing the filling aid (3) into the tube (1) in such a way that the lower end of the filling aid (3) is located at a first height, introducing catalyst particles (2) into the tube (1) to below the first height, optionally, partly withdrawing the filling aid (3) from the tube (1) so that the lower end of the filling aid (3) is located at a second or further height and introducing catalyst particles (2) into the tube (1) to below the second or further height, withdrawing the filling aid (3) completely from the tube (1) and filling the tube (1) with catalyst particles up to the final fill height.
 8. The method of claim 1, wherein the catalyst particles comprise shaped bodies which comprise a catalytically active composition.
 9. The method of claim 1, wherein the catalyst particles comprise a catalytic composition applied in the form of a shell to an inert support.
 10. The method of claim 2, wherein the catalyst particles comprise shaped bodies which comprise a catalytically active composition.
 11. The method of claim 3, wherein the catalyst particles comprise shaped bodies which comprise a catalytically active composition.
 12. The method of claim 4, wherein the catalyst particles comprise shaped bodies which comprise a catalytically active composition.
 13. The method of claim 5, wherein the catalyst particles comprise shaped bodies which comprise a catalytically active composition.
 14. The method of claim 6, wherein the catalyst particles comprise shaped bodies which comprise a catalytically active composition.
 15. The method of claim 7, wherein the catalyst particles comprise shaped bodies which comprise a catalytically active composition.
 16. The method of claim 2, wherein the catalyst particles comprise a catalytic composition applied in the form of a shell to an inert support.
 17. The method of claim 3, wherein the catalyst particles comprise a catalytic composition applied in the form of a shell to an inert support.
 18. The method of claim 4, wherein the catalyst particles comprise a catalytic composition applied in the form of a shell to an inert support.
 19. The method of claim 5, wherein the catalyst particles comprise a catalytic composition applied in the form of a shell to an inert support.
 20. The method of claim 6, wherein the catalyst particles comprise a catalytic composition applied in the form of a shell to an inert support. 